arXiv subjects

G. Bergmann

Publications and source records attributed to G. Bergmann.

112 records · Page 7Linked to original sources

arXiv2013

A directed search for continuous Gravitational Waves from the Galactic Center

We present the results of a directed search for continuous gravitational waves from unknown, isolated neutron stars in the Galactic Center region, performed on two years of data from LIGO's fifth science run from two LIGO detectors. The search uses a semi-coherent approach, analyzing coherently 630 segments, each spanning 11.5 hours, and then incoherently combining the results of the single segments. It covers gravitational wave frequencies in a range from 78 to 496 Hz and a frequency-dependent range of first order spindown values down to -7.86 x 10^-8 Hz/s at the highest frequency. No gravitational waves were detected. We place 90% confidence upper limits on the gravitational wave amplitude of sources at the Galactic Center. Placing 90% confidence upper limits on the gravitational wave amplitude of sources at the Galactic Center, we reach ~3.35x10^-25 for frequencies near 150 Hz. These upper limits are the most constraining to date for a large-parameter-space search for continuous gravitational wave signals.

gr-qc↗

arXiv2006

Measurement of the Geometrical Decay of the Spin Hall Effect in Fe(CsAu) Multi Layers

The anomalous Hall effect of Fe(CsAu) is investigated. Electrons with spin up and down experience a different degree of specular reflection at the FeCs interface. This yields a different mean free path for the two spin orientations. In the presence of an electric field parallel to the film plane one obtains a spin current in addition to the charge current. If one introduces impurities with a large spin-orbit scattering into the Cs host then the combination of spin current and spin-orbit scattering yields an anomalous Hall effect. By building in situ multi layers of CsAu (5nm of Cs and 0.04 atomic layers of Au) on top of an Fe film one can measure the relative magnitude of the spin current normal to the film. Within the accuracy of the experimental data the spin current in Fe(CsAu) decays exponentially with a decay length of 20nm. PACS: 73.50.-h, 72.25.Ba, 73.40.Jn, 73.21.Cd

cond-mat.mes-hall↗

arXiv2006

Severe discrepancies between experiment and theory in the superconducting proximity effect

The superconducting proximity effect is investigated for SN double layers in a regime where the resulting transition temperature T_{c} does not depend on the mean free paths of the films and, within limits, not on the transparency of the interface. This regime includes the thin film limit and the normalized initial slope S_{sn}= (d_{s}/T_{s})|dT_{c}/dd_{n}|. The experimental results for T_{c} are compared with a numerical simulation which was recently developed in our group. The results for the SN double layers can be devided into three groups: (i) When N = Cu, Ag, Au, Mg a disagreement between experiment and theory by a factor of the order of three is observed, (ii) When N = Cd, Zn, Al the disagreement between experiment and theory is reduced to a factor of about 1.5, (iii) When N = In, Sn a reasonably good agreement between experiment and theory is observed.

cond-mat.mes-hall↗

arXiv2004

The Superconducting Proximity Effect as a Tool to Investigate Metal Films and Interfaces

052 The superconducting proximity effect is measured in sandwiches of thin Pb films and the alkali metals Cs, Rb, K and Na. The $T_{c}$-dependence provides information about the interface barriers between Pb and the alkalis. Such a barrier is particularly large in Pb/Cs sandwiches. It is not due to impurities or oxydation. In the presence of a sufficiently strong barrier a special form of the Cooper limit can be applied to calculate the transition temperature of the sandwich.

cond-mat.supr-con↗